Gold rush = a bunch of fools getting hyped up on the latest thing thinking they’ll get rich, but almost none of them will.
Selling shovels = not chasing the latest hype, but making money off the fools who chase the latest hype.
Edit: because I know someone is gonna try this
That's not an opinion or an interpretation. That's the meaning of the phrase. It's not this amorphous ambiguous thing where all interpretations are valid. It has a specific meaning.